The respiratory system is one of the major interfaces between the body and the external environment. As a result, it can become a target for a broad range of environmental agents that can lead to increased morbidity and mortality. The medical field has also exploited the respiratory system/air interface as a way for either targeting drug delivery to specific regions of the respiratory tract or to provide rapid access to the systemic circulation for drugs that may not be effectively administered by other means. Furthermore, various diseases, such as COPD, or interstitial lung disease, can alter the structure and function of the respiratory system and dramatically affect how airborne agents or drugs are inhaled, deposited, or absorbed. Computational models that can effectively predict the dosimetry and ultimately the consequences of exposure to airborne agents under healthy or disease conditions in either animals or humans do not exist. As a result, this Bioengineering Research Partnership is developing the imaging and computational tools necessary for constructing and validating state-of-the-art, biologically based, multi-scale computational models of the respiratory system that incorporates the inherent species differences and heterogeneities in structure and functional relationships and the influence of disease on airflows and dosimetry predictions. In this way, computational predictions can be more rigorously tested and have a broader impact on human health risk assessments and therapeutic interventions. In light of increasing interest in nanomaterials for medical applications as well as concerns over potential human health risks, our model validation studies will focus on particulates utilizing our novel 3D imaging approaches. Our specific aims are therefore organized around model development, experimental evaluation, and model refinement to predict: a) site-specific airflows in health rats (Aim 1); b) site-specific airflows in rats with interstitial lung disease and COPD (Aim 2); c) aerosol deposition in healthy and diseased rats (Aim 3); and d) aerosol deposition in healthy and diseased humans (Aim 4). Ultimately, we expect to deliver realistic, comprehensive, predictive models of the respiratory system that incorporate the inherent heterogeneities in anatomy, physiology, and disease. In addition, this effort will provide researchers and clinicians with a unique suite of imaging and computational tools for understanding species-specific pulmonary structure-function relationships and their effects on particle deposition and clearance.